Add exercise 4.46

mceval/amb-natural-language.rkt

@@ -152,3 +152,16 @@
                                                         (article the)
                                                         (noun cat)))))))))
 ;; The professor lectures to the student, who is in the class with the cat
+
+
+;; Exercise 4.46
+
+;; If amb evaluated its arguments in any order other than
+;; left-to-right, then the recursive maybe-extend rules would never
+;; terminate, as the second argument is a recursive call to the
+;; procedure.  We rely on the recursion stopping at each decision
+;; point.
+;;
+;; Also, since parse has side-effects (namely, it removes a word from
+;; the input), it is important that we parse the different parts of
+;; the sentence in the correct order.